Port mate-search-tool to Gsettings

This pull request converts mate-search-tool to use gsettings instead of MateConf. It checks if the caja schema exists before loading caja preferences in order to prevent crashes. (caja defaults are used if the caja schema doesn't exist).

Based on:
http://git.gnome.org/browse/gnome-search-tool/commit/?id=e70bc86ed2f4953d6f0469a3c3009e99265dd984
http://git.gnome.org/browse/gnome-search-tool/commit/?id=ec33dd71ab594a8adbe067049fe2b7efc2a4a4be
http://git.gnome.org/browse/gnome-search-tool/commit/?id=89e15af10b20953ab11db3b10b0510b7cdeef7b8

and some bug fixes:
http://git.gnome.org/browse/gnome-search-tool/commit/?id=c8f3b8834e487feb9885bbf1051189ee1ac96ae9
http://git.gnome.org/browse/gnome-search-tool/commit/?id=c4cd0f20fc949689ee64bb1a5650a5683eaf3d00
http://git.gnome.org/browse/gnome-search-tool/commit/?id=6e650f021bac5134e15b129e26c888bc4fc88075